This invention relates to offshore oil production apparatus and, in particular, to a tieback tool and method for connecting a tieback conductor (also referred to as tieback casing) to a subsea well.
Offshore oil wells may be drilled from a drilling vessel or rig and thereafter produced to a fixed platform. Typically, once a well is drilled to depth, it is plugged, a protective cap installed and the drilling vessel moved to another well location. The fixed platform is then moved to a position over the well, the cap removed and tieback conductors are run from the platform deck to the well. Tubing is then run, surface production trees installed, and the well produced in the conventional manner.
A complication comes about, however, because it is nearly impossible to align the fixed platform precisely over the well system and although the tieback conductor string runs through the guides at various elevations, offset still occurs and the problem is particularly acute where there is angular misalignment in the vicinity of the well system where the tieback conductor is to be joined to the well.
Funnels have been used in tieback tools to overcome the alignment problem and prevent damage to threads either in the well system or in the tool as they were being engaged as shown, for example, in U.S. Pat. Nos. 4,343,495 and 4,408,782. These funnels aligned the tool with the well system prior to engagement of the mating threads. After alignment, additional tools were used to thread the tieback tool into the system and to activate the seals therein. Even with such a funnel and additional tools, the existing tieback tools cannot be engaged if there is a large angular misalignment in excess of 2.degree. and attempts to make up the joint with such misalignment resulted in improperly loaded threads and galling thereof.